In a manufacturing process of a semiconductor device or a manufacturing process of a flat panel display (FPD), a process of performing processing by supplying a processing liquid to various substrates such as a semiconductor wafer or a glass substrate is frequently used. Examples thereof may include a cleaning process using various kinds of processing liquids for removing particles attached to the surface of a substrate or a native oxide layer formed by contact with the atmosphere.
A substrate processing apparatus performing a process such as a cleaning process as described above on a substrate is used, which includes a plurality of substrate processing units of a single wafer type and a transport unit. The transport unit carries-in/out a substrate into/from these substrate processing units.
The substrate processing unit includes, for example, a rotary table, a plurality of holders and a nozzle head. The holders are installed on the rotary table in plural and hold a circumferential edge of a substrate which is disposed on the rotary table by the transport unit. The nozzle head is positioned on a top surface side of the rotary table and supplies, for example, a processing liquid on a top surface of the substrate disposed on the rotary table.
Some of the substrate processing apparatuses have a detector for detecting a holding state of the substrate held by the holders (see, for example, Japanese Patent Application Laid-Open No. 2003-229403). The detector includes a light source and a light receiving element. The light source emits light including, for example, a laser beam and is disposed above the rotary table outward in a diameter direction of the rotary table. As in the light source, the light receiving element is disposed above the rotary table outward in the diameter direction of the rotary table. The light receiving element is disposed such that light, which is irradiated from the light source and reflected from the top surface of the substrate, is incident on the light receiving element, and a holding state of the substrate is detected by detecting an angle of the substrate held by holders with respect to the horizon based on a variation in light amount of light which is incident on the light receiving element.